This invention relates generally to fiber optic connection systems and, more particularly, to a connection system comprising a fiber optic cable terminal and a header for connecting the terminal to an electro-optical device or other cable.
Optical fibers used for data transmission are most often supplied in cable form in which the cable comprises a pair of jacketed fibers carried within a protective sheath. Each jacketed fiber comprises a plastic fiber core, a thin cladding, and a protective jacket which can include strain relief fibers.
Connecting the fiber optic cable to electro-optical devices or other cable requires the provision of a terminal on the cable end. The termination of the cable is often performed as a field operation, such as when installing data transmission systems, such as computer LANs (Local Area Networks).
To provide a durable and optically efficient interface between a fiber end and an electro-optical device, it is preferable to mount the fiber end in a suitable terminal connector in a manner that will provide good signal transmission. It is also necessary to properly and reliably align the fiber ends and engage the ends with the electro-optical devices to enable effective data transmission across the interface.
Many different connection systems have been developed to connect optical fiber ends with electro-optical devices. One such system is shown in U.S. Pat. No. 4,678,264 to Bowen et al in which a cable containing both electrical and optical fibers is provided with a terminal in which the fibers are adhesively mounted. This connector is then inserted into a header mounted on a circuit board and latched by connector lock tabs which engage mating header slots.
This arrangement has several shortcomings. There is no provision to bias the terminal ends into engagement with the devices to assure a good optical interface. The adhesive mounting of the fiber end in the terminal must be carefully performed to prevent fouling of the fiber end with adhesive and is not suitable to field use. The disclosed arrangement is unduly complex and, therefore, expensive.
Another connection assembly is illustrated in U.S. Pat. No. 4,875,755 to Burgos et al. A cable is inserted through a flexible boot which fits in a housing. The cable is stripped and the two fiber ends are inserted into and cemented in ferrules that are retained in spaced cavities. Electro-optical devices are mounted in a cover plate which is screwed onto the housing. Compression springs in the cavities bias the ferrules into contact with the electro-optical devices.
While this arrangement provides for biasing the fiber ferrule ends into contact with the electro-optical devices, it requires the provision of two discrete compression springs. It again requires the use of adhesive. It also is an expensive and complex assembly.
An improved connection system is disclosed in U.S. Pat. No. 4,993,803 by Suverison et al and assigned to the assignee herein. A ferrule is clamped to a fiber jacket and the fiber end is processed. The ferrule is slidable in a two-part terminal body. The terminal is inserted into a header housing an electro-optical device and latched. A compression spring biases the ferrule to contact the fiber end with the device. The terminal and header also carry electrical contacts. A separate spring is required for each fiber ferrule.
A simpler connection system is shown in U.S. Pat. No. 4,479,696 to Lubin et al. Here a single fiber is mated to a single electro-optical device mounted in a pocket of a header. The header contains a bifurcated extension that includes a receptacle for a fiber terminal fitting. The fitting has a peripheral frusto-conical rib which is engaged by mating surfaces on the header upon forcing of the terminal into the receptacle to a position adjacent the electro-optical device. The mating header surfaces are so positioned as to exert a wedging force on the rib. The axial component of this wedging force biases the terminal fitting into engagement with the device. How the fiber is mounted in the terminal is not disclosed.
Although this arrangement eliminates springs, it presents a paradox. There is no positive latch. The only force maintaining the terminal in contact with the header is the axial component of the wedging force. If this force is to be substantial, so will be the force required to insert the terminal. Since the method of mounting the terminal on the fiber optic cable is not disclosed, the problem of dealing with the substantial axial stress inherent in inserting the terminal in the header is not addressed.
To enable the widespread use of fiber optics in data transmission, it is necessary to simplify the connection system and to provide one which is both economical and reliable. There is a distinct need for a simple and inexpensive connection system for mating the end of an optical fiber with an electro-optical device. There is also a need for a simple, inexpensive and effective terminal connector for a fiber optic cable.